1. Field of the Invention
The present invention relates to broadband signal switching equipment and is particularly concerned with broadband signal switching equipment comprising a crosspoint matrix constructed in accordance with field-effect transistor (FET) technology.
2. Description of the Prior Art
If emitter-coupled logic (ECL) technology can be characterized by properties such as high working speed, minimum-to-high packing density and medium-to-high power dissipation, then field-effect transistor (FET) technology, given, however, only medium working speeds in comparison thereto, is distinguished by extremely-high packing density and very low power dissipation. These latter properties lead to the efforts to advance into speed regions with integrated circuits in FET technology that were heretofore reserved for bipolar technology.
For a broadband signal switching equipment having a crosspoint matrix that comprises respective matrix input lines formed with two signal conductors which, on the one hand, are respectively connected to two difference (complementary) outputs of an input digital signal circuit and, on the other hand, are connectible via crosspoints to matrix lines that are likewise respectively formed with two signal conductors that respectively have their two signal conductors leading to the two signal inputs of an output amplifier circuit formed with a differential amplifier, a crosspoint matrix constructed in accordance with FET technology, respectively having pairs of coupling elements provided in the crosspoints and formed with respectively two switching transistors charged with a through-connect signal or, respectively, an inhibit signal at their control electrodes is known in this context, for example from the European application 0 264 046 whose switching transistors respectively have the main electrode connected to the one signal conductor or, respectively, to the other signal conductor of the appertaining matrix output line that is, in turn, provided with an output differential amplifier having a trigger behavior, whereby the pairs of coupling elements respectively comprise two auxiliary transistors that each respectively form a series circuit with a switching transistor,
these auxiliary transistors respectively having their control electrodes connected to the one signal conductor or, respectively, to the other signal conductor of the appertaining matrix input line and the respective main electrodes facing away from the series circuits connected via a sampling transistor to the one terminal (ground) of the operating voltage source and having their other main terminal connected to each signal conductor of the respective matrix output line via a respective pre-charging transistor,
and whereby the pre-charging transistors and sampling transistors have their respective control electrodes charged opposite to one another when a switching matrix network drive clock that sub-divides a bit through-connect time interval into a pre-charging phase and into the actual through-connect phase, so that both signal conductors of the matrix output line in each preliminary phase given an inhibited sampling transistor are charged via the respective pre-charging transistor at least approximately to the potential prevailing at the mentioned, other terminal of the operating voltage source.
In addition to the advantages that are involved in a crosspoint matrix constructed in accordance with FET technology, this known broadband signal switching equipment produces the further advantage that, given an inhibited crosspoint, no disturbing signals, on the one hand, proceed via the crosspoint to the matrix output even without additional attenuation measures and that, on the other hand, given a conductive crosspoint, charge reversals of the matrix output line that may potentially occur in the actual bit through-connect condition always proceed from the one operating potential corresponding to the one signal state in only one charge reversal direction and, therefore, an unambiguous transition of the through-connected digital signal appearing at the output of the switching equipment from the one into the other signal state already occurs with a small charge reversal (corresponding to the transgression of a threshold adjacent to this value of an operating potential and corresponding to the break-over point of the differential amplifier), and, therefore, correspondingly fast.
A further enhancement of the operating speed in such a broadband signal switching equipment can be enabled in that the two pre-charging transistors have their main electrodes that respectively face toward the matrix output line connected to one another via a transverse transistor whose control electrode is connected to the control electrodes of the pre-charging transistors, as in the German patent 38 19 491; in combination with the advantage of accelerating the pre-charging of the matrix output lines, this yields the further advantage of an extremely-early balancing of the potential of the matrix output lines, so that the starting conditions for a reliable amplification by a following differential amplifier are established correspondingly early.
A further enhancement in the working speed of the broadband signal switching equipment is obtained when, in addition to a sampling transistor individually associated to the matrix input line, a pre-charging transistor individually associated to the matrix input line is provided or, alternatively, a pre-charging transistor individually associated to the matrix output line is provided in addition to a sampling transistor individually associated to the matrix output line in accordance with the German patent 38 19 491.
The advantages of such a known broadband switching equipment that can be obtained in view of dissipated power consumption and operating speed, this broadband switching equipment respectively comprising matrix input lines formed with two signal conductors, are involved with a corresponding space requirement for such respectively two signal conductors of the matrix input lines.